Typewriter paper of deferred indelibility and method of preparing the same



March 19, 1935. g 1,994,750

TYPEWRITER PAPER 0F DEFERRED INDELIBILITY' AND METHOD PREPARING THE SAMEFiled Sept. 23, 1935 Patented Mar 1 earns or nnrnnnnn mnnarnrrr awnrm'rnon or rare "t 'l in THE S .lio G. Calian, @ambridge, Mass.

This invention relates to writing paper of the several classes that areintended principally as typewriter papers for receiving typewriting bythe impressions of the raised type either from the inked ribbon or fromcarbon paper. The

paper of this invention is as well suited as are most writing papers forreceiving markings from pen and ink or from lead pencil, but theadvantages that it possesses relate more particularly to its use as atypewriter paper.

The objects of the invention are as follows: To produce a paper fromwhich recent typing can be erased easily, quickly and practicallycompletely by means of a pencil eraser of soft rubber or the compositionknown as art gum without resort to a sand rubber containing abrasivesuch as is commonly used for erasing typewriting:

Tomake it possible to erase several times in the same place in themanner described:

To provide that although the recent inked im- I pression can be wipedoif easily with soft rub-. her or art gum and without noticeabledefacement of the surface, it shall nevertheless be ad herent enough sothat it cannot be wiped 013 nor easily smeared by casual friction fromother substances:

To avoid any requirement for" special typewriter ribbon or specialcarbon paper not already in prevalent use, and to assure the statederasing properties for red impressions as well as black:

To insure that with passage of time a typed record on the said papershall become progressiveiy harder to erase so that it shall eventuallyacquire enough resistance to erasure to constitute the said record asafe one that cannot be altered or removed without the vigorous use ofsuch customary erasers as the sand rubber,'which so disturb and defacethe surface of the paper that it is possible to ascertain that a changehas been made.

It is well known that writing papers made of difierent substances andmade and finished in different ways show widely different degrees ofresistance to erasure, but so far as this applicant. knows, all of themrequire the'use of an abrasive rubber or equivalent to eradicate thetyped impression. it may therefore be emphasized that the firsto'bjectof this invention contemplates an erasure wherein the fresh impressioncan be wiped cleanly from the surface in a manner difiering in more thandegree from that characterizing even the more easily erasable papers ofthe prior art.

In accordance with the present invention, those constituents of thepaper sheet capable of receiving a relatively permanent mark from the"of top sizing.

s, 1933, Serial No.69llfld2 ink are protected from immediate contacttherewith, afterthe ink has been applied, by other constituents. Inorder to confer ultimate indelibility these other constituents are ofsuch character as to be progressively and ultimately so com- 5 pletelypenetrated by the ink, or by certain of its constituents capable ofproducing a relatively permanent mark, as to render the mark effectivelyindelible.

I have found that all of the objects that have 10" been specified areaccomplished very satisfactorily by process and means that will next bedisclosed. Wherever possible the requirements will be defined along withpreferred means for meeting them.

For a more complete understanding of this in;- vention reference may behad to the accompanying drawing in which is represented in perspective,and much magnified, a fragment of a sheet of paper treated in accordancewith this inven- 2 tlon. All the objects are met if the surface of thepaper on which the writing is to appear is evenly covered by a scum orfilm of a material'of properties that will be defined, laid on muchthinner than the coating of ordinary coated papers, following the minutesurface irregularities, hills I and hollows, and coating them withoutobliterating them to any such degree as is usual with coated papers, andpenetrating the porous suro face of the paper to a controlled andlimited degree, much less than that sought in the operation As apractical matter, however, both faces of the paper will ordinarily be sotreated, partly because either side can then be equally well printedupon, and also because if the paper be treated on one side only it mayShow some tendency to curl, while with both sides alike this tendency isnot found. Such a film is indicated at 1 on the drawing, on oppositefaces of the paper 2. v

The properties of the materials suitable for forming this filmintermediate between a coating and a top-sizing, should be as follows;

The material should be one that can be applied from solution ordispersion, preferably water dispersion, and dried on the surfaces ofthepaper; that will form on the paper surface a thin protective film orscum that shall have such' inherent properties,.and that shall be sorelated to the m superficial layers of the paper, as to kiep the ink ofthe typed impression from coming at once into direct contact with thecellulosic paper substance itself; and that shall be only slowlypermeable to miss ordinarily used on typewriter ribbons and carbonpapers, but shall eventually allow such inks or constituents thereof topenetrate it by diffucion, or otherwise, and reach the paper andpermeate, stain or mark the paper itself.

There are several materials that meet the requirements andare notprohibitively expensive; casein,preferably with additions itsink-permeability is one suitable one, and the preferred proportions ofthe mixture will be described hereinafter.

The physical relation of the protective dilm to the paper-substance isimportant, and a preliminary statement of the two extremes to avoid willhelp define the limits between which .good results are found. Ordinarycoatings are commonly applied for the purpose of giving a smoother andmore glossy and specular surface for receiving halftone printing or forother uses by filling in the minute superficial depressions in thefelted mass of paper fibres. This will not serve the purpose of thisinvention, because the desired film should cover each paper fibre toabout the same thickness so that the eventual penetration of the ink tothese fibres (insuring eventual permanence of record) will proceedevenly and not be spotty. Early experiments with thick coatings showedthis point to be an important one. Furthermore, such filler coatingscontain sucha large proportion'of mineral matter such as clay or thelike, that surface finish of the paper is destroyed by even lightrubbing with a soft rubber. On the other hand, where sizing material,even in excess of the usual amount, is applied hot,'and the excessimmediately removed by squeeze-rolls, as it is in the top-sizing ortub-sizing operation as commonly practiced in paper-sizing, the hotsizing liquid sinks into the paper structure like butter on very hottoast, and leaves the protuber-' ant tops of the fibres so thinlycovered that the typewriter ink finds access to them at once and theoperation does not confer the necessary sort of complete initialerasability that'is desired; it makes erasing with a sand-rubber easier,as is well known, but so far as this applicant's experiments havedeveloped the facts, and so far' as can be judged from many examples ofheavily top-sized paper's, it never makes a surface from which a'newtyped impression can be cleanly wiped by the use of asoft rubber. Thetwo extremes or boundaries in procedure that are to be avoided, havingthus been pointed out, the desired effect or result, and the preferredmeans of obtaining it, may the better be defined. The surfacing materialshould be applied as a cold solution or dispersion well evened over thesurface, leaving enough so that the is distinctly wetncl; merely verydamp. There is some latitude as to the thickness of the solution ordispersion to be used, but its character should be such that eitherinitially or with progressive .-drying it becomes gelatinous rather thanmerely viscous, so that once it coats the tops of the very minuteprotuberant fibres characterizing the surthan the hollows between them.Examination under a strong magnifying glass of colored films in processof drying shows that with a suitable residuum of a propersurface-filmingsolution this evenness can be well accomplished ifthejfilm is dried, as it should be, free from substantial surfacepressure and without application of such heat as would confer flowing orleveling properties on the wet surfacing material before it has a chanceto "scum over" and establish sumcient form-stability so that subsequentdrying will not materially disturb the evenness of the application. Thislast named condition is well fulfilled by the well known air blastdrying used on paper-coating machines which apply coating on both sidessimultaneously and "fioat the wet coated paper on a seriesof upwardlydirected streamsof air emerging from a blower-trimk of rectangularsection above which the paper fioats untilit is dry enough to be hung infestoons without adhering to the wooden sticks.

4 If the paper is not well-sized prior to this scumming or filmingoperation, it is absorbent, and a part of the solution or dispersion offilming material soaks in with the undesirable results of increasingexpense, and, mor important, of tending to give irregularity of efinally remaining protective surface. Experience has shown thatasuitable degree of initial sizing will result from the use of the usualamount of rosin size in the beater, varying with different grades ofpaper and following good current practice, and a final "top-sizing" withthe material known in the trade as Hercules gum" of 5 concentration'rather than the 2 concentration that is in more, common use. There issome latitude in these proportions, and glue-size of equivalentconcentration may be substituted for the ercules gum". The resultingprotective scum, f a thickness that appears from weight of added terialto be of the general order of one to two tenths of a mil (0.000Ito0.0002 inch), must be practically continuous so that it shall not leaveexposed pin-holes that give access forthe ink to the paper-substancebeneath. If the film is well formed, a very slightly moist piece of thepaper, on being held above a flaming match, will form a blister orballoon in which the steam, unable to escape, splits the paper into twolayers; when this testis made it ing paper, and has been wellcalende'red on the paper machine.

Another convenient test for the minute uncovered or insufiicintlycovered spots called pinholes consists in flowing gasoline over thesurface of the sample and noting any progressive formation oftranslucent grease-spots" resulting from penetration of the gasolinethrough such pin-holes into the untreated interior of the sheet. Thesize and rate of growth of such greasespots when the surface iscovered'with a film of gasoline gives'a quick and very searching 'meansof estimating the continuity of thesurface film. Their number'and sizeshould be relatively small after 20 seconds, but if there are none, itusually indicates that the scum is so thick that while the initialerasing properties will be excellent, the penetration of the typewriterink with passage of time .will be slow. The operator soon learns tocorrelate test performance on the typewriter with this indication,

It will be understoodthat this protective film closely follows theminute hills and hollows of the interlaced fibres of the paper, andmaintains as nearly as possible aneven thickness over'the whole contour,as shown by the drawing. The protective material seems to penetrate andfill such very small or narrow .fissures between fibres as are somewhatparallel-sided and-of capillary dimensions, as indicated at 3 in thedrawing, but-so far as microscopic examination is able to show, itfollows vwell the other irregular contours if the precautions indicatedhave been observed, and if the preferred solution and method or theirequivalents are used,' as specified hereinafter. There is some shallowpenetration of the surface, largely in the nature 'of such filling ofmicroscopically narrow interstices and crevices as described, but with aproperly sized sheet, well machine-calendered, this capillary absorptionis small and the addition of weight due to the protective scum onwriting paper of 20 pounds ream weight should be between 5% and withabout 7 as the normal value to be taken as standard for two-sidecoating.

The scum or film may consist of any material that has the propertiesthat have been defined. Excellent results have been obtained withfilmforming colloids as, for example, casein, hardened and preventedfrom becoming sticky with moisture by addition of formaldehyde, andpreferably made somewhat more quickly penetrable to oilbase typewriterinks by addition to the solution of some material such as sulphonatedcastor oil or soap, that oil will wet more readily, and diffuse throughmore rapidly, than is the case with a film of casein alone. Experiencehas shown, however, that a film of casein hardened with formaldehyde andwith no other additions gives excellent initial erasure, and givesenough time-penetration to insure the appearance within two or threedays of an impression of the typed letters in the papersubstance, ratherfaint, but not erasable with anything less drastic than a sandrubber-.Special copying ribbons with glycerin or other watersoluble oralcohol-soluble involatile material as the agent for maintainingprinting qualities, penetrate fairly rapidly through casein filmswithout admixtures, but the admixtures do not prevent this penetrationof impressions from such unusual inks. Of promoters of penetration ofthe nearly universal Vaseline-base inks, either sulphonated castor oil(Turkey-red oil), or a pure soap, in quantities that will be specified,cause the impression that eventually appears in the paper substance tobe heavier, and somewhat accelerate the appearance of that impression.Of the two, the soap is rather the more effective in promoting boththese purposes, and it is not objectionable in any respect known to thisapplicant unless it should tend to cause yell-owing in the paper afterthe passage of much more tirne than has been so far occupied by theexperiments.

Among alternative materials gelatin, and its equivalent, glue, hardenedby any of the wellknown tanning agents used in hardening gluesize, havebeen tried with good results. The glue film is rather less penetrable toVaseline inks than a casein film, and the glue solution is much moreintractable to handle in the machine. while there are no markedadvantages. over casein for the purposes of this invention- Starchcooked in the ordinary manner forms an excellent film, somewhat softerand less resistant to repeated erasures than hardened casein ortannedgelatin or glue, but presenting a material 'quite satisfactory andbut little inferior to the other two.

There are many formula: for the ink for type- .writer ribbons and carbonpapers, andalconsiderable number of dyes and mixtures of dyes is foundeven in black ribbon. Thus far allthe ribbons and carbon papers triedhave shown the desired results, although with some black mixtures,especially when sulphonatedjcastor oil is used in the film as the mediumfor promoting ink diifusiom,

a purple component shows preferential diffusion and the deferredrelatively indelible impression on the paper substance, after erasingwhat a soft rubber will still remove after passage of time, is found tobe purple instead of black. In so far as inks which do not contain dyesare concerned, and when the protecting coating on the paper contains nopenetrant, the indelible mark from the ink appears initially as smallblack dots which gradually increase in size and number and onmagnification give somewhat the appearance of the spots of the gray partof a half-tone print. At least in those instances where no penetrant isemployed in the coating, an important factor in the development ofindelibility appears to be the capability of the film through itsinherent fragility to have its continuity locally,impaired as throughincipient cracking or shattering under the blows of the type, developingnumerous slight localized discontinuities through which the ink maygradually pass to the paper beneath. While the heaviness of the touch ofthe operator on the typ writer keys is of some eifect in determining thetime of ultimate indelibility of any particular paper treated inaccordance with this invention, the nature of the impact of the typeagainst the paper is found to be of much more importance, it beingpossible to use a thinner protective coating satisfactorily ith theso-called noiseless machines where the impact of the type is in thenature of a pressure than with other machines where the type strikes asharp blow.

One coatingsolution that has given excellent results is as follows: Acasein solution is made by adding casein to cold water in the proportionof 1% pounds of casein to each gallon of water. The casein is allowed tosoak in the cold water for one to two hours and the mixture is thencooked as in preparation of caseinjor coating; at some time during thecobking either borax or ammonia are added in proportions well known, tocut the casein. This cooked solution is allowed to stand at robmtemperature for about 12 hours, whereby its physical character becomesmore gelatinous and less viscous. The working solution,-or dispersion,ismade by diluting this with water, and here there is some latitude;excellent results have been attained with a concentration reached byadding 20 gallons of water to 15 gallons of the strong casein solution,and adding thereto 2 quarts of commercial (50%) formaldehyde. To this isadded the amounts of color and china-clay that will give the film thedesired appearance and tint, and the whole is very thoroughly mixed. Ifit is desired to accentuate the strength of the indelible impressionthat will eventually be'developed, as it commonly will be, there is thenadded either of the following: cubic centimeters of sulphonated castoroil for each litre of solution or 25 grams of a pure soap, free fromuncombined alkali. The soap is less expensive, and. gives results asgood in all respects aside from'some apprehension of possible Thetreating material can be applied in any way There are also vathat willinsure the formation of a continuous and very thin sufliciently cohesivefilm following the minute contours of. the irregular paper surface. Thepreferred method is by the use of a coating machine, the aqueousdispersion being spread while at about room temperature. The initialdrying or setting is effected cold, at or below room temperature, thoughthe final drying after the film has been formed may be 'by heat, ifdesired, as in the usual paper coating operation. The coating machinemay well be one having a roller feed and a pair of oscillatory brushesfor evening the coating. It is preferable to cover both sides at onetime on a two-side coating machine of wellknown type where the paper isfloated on up wardly directed successive jets of air during the initialperiod of the drying up to the time when it is no longer sticky.However, excellent paper has been made on a machine covering one side ata time; with this form, curling in process of manufacture makes handlingdifiicult.

I claim:

1. 'A sheet of typewriter paper including sizing material constituting athin coating of even thickness following surface irregularities of thepaper and capable of receiving ink from a typewriter type impressibn andfrom which said ink is initially easily erasable without noticeabledefacement of the sheet, but which coating permits slow penetrationtherethrough of constituents of said ink capable of indelibly markingconstituents of said paper, whereby said typewritten impression becomesprogressively indelible.

2. A sheet of typewriter paper having a surface sizing coating ofsubstantially even thickness following the surface irregularities of thepaper and of such thickness as to initially prevent a typewritten inkimpression on said paper from reaching constituents of the paper capableof receiving an indelible impression therefrom but sufficiently"thin topermit constituents of such ink to gradually penetrate such coating andprogressively render said impression indelible.

3. A sheet of typewriter paper having a sizing coating applied theretounder such controlled conditions as to produce a coating of eventhickness following surface irregularities of the paper and sufiicientlythin so that a typewriter ink impression made on said coated paper isinitially easily erasable but progressively'becomes indelible.

4. A sheet oftypewriter paper having a sizing coating applied theretounder such controlled conditions as to produce a coating of eventhickness following surface irregularities of the paper and suflicientlythin so that a typewriter ink impression made on said coated paper isinitially easily erasable but progressively becomes indelible, saidcoating being of a character which initially receives the ink withsufficient adherence to resist smearing.

5. A sheet of typewriter paper having a sizing coating applied theretounder such conditions of temperature and viscosity as to produce a thinsuperficial coating of even thickness following surface irregularitiesof the paper and resistant to penetration of typewriter inktherethrough, so that a typewriter ink impression made on .said paper isinitially' easily erasable but progressively becomes indelible.

6. A sheet of typewriter paper having a sizing coating applied theretounder such controlled conditions includingthe viscosity of such sizingas to produce a thin superficial coating of even thickness of the orderof .1 to .2 of a mil sufiiciently-resistant to penetration of typewriterink therethrough so that a typewritten impression on said coated paperis initially easily erasable but becomes progressively indelible as theink penetra-tes said coating and stains the paper substance beneath saidcoating.

7. A sheet of typewriter paper having a sizing coating applied theretounder such conditions of temperature and viscosity as to produce a thin'superficial coating of substantially even thickness of the order of .1to. .2 of 9. mil substantially following surface irregularities of thepaper, said coating having suflicient cohesion and being suflicient lyresistant to the penetration of typewriter ink therethrough so that atypewritten impression on said coated paper is initially easily erasablewithout noticeable defacement of said coating but becomes progressivelyindelible as the ink penetrates said coating and stains the papersubstance beneath said coating.

8. A sheet of typewriter paper having a superficial substantia ycontinuous protecting coating of substantia ly even thickness followingsurface irregularities of the paper and capable of initially receiving atypewritten ink impression and of suflicient fragility to be locallyimpaired under impact ofa typewriter type to an extent.

sufiicient to permit said ink gradually to pass writer ink and fragileenough to develop numer- 'ous slight localized discontinuities underimpact of a typewriter type. v

10. A sheet of typewriter paper having a casein coating applied theretounder such controlled conditions as to produce a coating of eventhickness following surface irregularities of the paper and sufiicientlythin so that a typewriter ink impression made on said coated paper isinitially easily erasable but progressively becomes indefible. P

. 11. A sheet of typewriter paper having a starch coating appliedthereto under such controlled con'ditions'as to produce a coating ofeven thickness following surface irregularities of the paper andsufliciently thin so that a typewriter ink impression made on saidcoated paper is initially easily erasable but progressively becomesindelible. a a

12. A sheet of typewriter paper having a tanned glue coating appliedthereto under such controlled conditions as to produce a coating of eventhickness following surface irregularities of the paper and sufficientlythin so that a typewriter ink impression made on said coated paper isinitially easily erasable but progressively becomes indelible.

13. A sheet of typewriter paper having a sizing 14. The method oftreating paper, which comprises applying a liquid coating size theretoand drying the same under such controlled conditions as to produce acoating of even thickness following surface irregularities of the paperand smilciently thin so that typewriter ink applied thereto is initiallyeasily erasable butprogressively becomes indelible. 15. The method oftreating paper, which comprises applying a liquid coating size theretowhile in a somewhat gelatinous condition and drying the same free fromsubstantial surface pressure delible.

and during initial setting at sufficiently low temperature so as toproduce a coating of even thickness and sufilciently thin so that atypewritten ink impression on the-coated paper is initially easilyerasable but progressively becomes 'in-' 16. The method of treatingpaper which coinprises applying, while in 'a somewhat gelatinouscondition, a liquid coating size selected from a group consisting ofstarch casein and glue, and drying said coating free from substantialsuris initially easily erasable but progressively be- 10 comesindelible. v

JOHN G. CALLAIL-

